Fail-safe film prewinder for cameras

Abstract

A fail-safe film prewinder for a camera. The prewinder has a mode switch which can be changed over by switching to a photographing mode upon completion of a prewinding mode in which a film is continuously pulled or prewound from a film cartridge loaded in the camera. When the mode switch is in the prewinding mode position while a shutter release button is being operated, a film transport motor is rotated in the direction to prewind the film again after an interruption of the prewinding mode.

We claim: 
     
       1. A fail-safe film prewinder for a camera in which film is continuously prewound from a loaded film cartridge in a film prewinding mode and thereafter is successively exposed in a photographing mode while the film is rewound one frame at a time into the film cartridge, said fail-safe film prewinder comprising: a film transport motor rotatable in opposite directions for selectively transporting the film out of and into the film cartridge;   a mode switch for switching to the photographing mode upon completion of the prewinding mode;   a release switch actuatable in response to the depression of a shutter release button; and   a motor controller for controlling said film transport motor by producing a first signal in controlling the motor to rotate in the direction to prewind the film out of the film cartridge when said mode switch is in a prewinding position and a second signal controlling said motor to rotate in the direction to rewind the film into the film cartridge when the mode switch has been switched to the photographing mode; said motor controller also producing said first signal in response to an interruption in the prewinding and said shutter release switch being actuated by said shutter release button.   
     
     
       2. A fail-safe film prewinder according to claim 1, wherein said mode switch has a movable contact which can be shifted in response to a change in the tension to which the film is subjected. 
     
     
       3. A fail-safe film prewinder according to claim 1, wherein said mode switch doubles as a switch for detecting the loaded film cartridge. 
     
     
       4. A fail-safe film prewinder according to claim 1, further comprising an interruption detecting circuit for detecting the reduction of the power supply voltage below a reference voltage and indicating to said motor controller the occurance of an interruption.